Torque delivering pulse power tools include a pulse unit that intermittently connects a motor shaft to an output shaft that is arranged to hold a tool implement. The pulse unit comprises a housing in which a cylinder is arranged to rotate. The cylinder is driven by a shaft that is driven by a motor, directly or via a gear. An anvil is arranged inside the cylinder and is intermittently driven, i.e. in pulses, by the cylinder.
Together the cylinder and the anvil form a pulse unit. There are different types of pulse units. There are piston pulse units and there are vane pulse units. In both these types a non-compressible, or close to non-compressible, hydraulic fluid is utilised as an intermediate in the generation of pulses between the components of the pulse unit.
A problem in pulse tools is the wear of the parts of the pulse unit. The wear will produce particles which in turn may lead to further wear. Air bubbles in the fluid are also harmful and may cause wear.
In WO 2011/141205 a power tool with a piston pulse unit is described. In this power tool an air separator element is arranged to remove harmful air bubbles in the fluid. The air bubbles are harmful in that their presence in the hydraulic fluid affects the properties of the hydraulic fluid and makes it compressible which in turn reduces the efficiency of the pulse unit and contributes to further wear of the moving parts of the pulse unit. In a specific embodiment in WO 2011/141205 the air separator is also provided with a filter for removing particles from the fluid.
Filters of this kind for removing harmful particles have a proven effect but problems relating to long term wear of the pulse unit are not eliminated, since the particles may wander about in the system a while before they end up in the filter.
Hence, there is a need for a construction in a power tool that helps reducing the long term wear of the parts of the pulse unit.